In the field of inks and dyes, there are several applications for fluorescent inks and dyes and combinations of fluorescent inks and dyes having disparate or complementary frequency responses. Various security and anti-tamper and authentication solutions making use of fluorescent or otherwise photo-responsive inks are currently known, but they have deficiencies that enable them to be readily counterfeited or otherwise circumvented. Fluorescent or similarly photo-responsive dyes are typically used so that the photo responses of the dyes do not overlap or are otherwise readily visibly distinguishable during simultaneous or single-source illumination. It would be a significant advantage, however, to leverage multiple photo-responsive materials to create a visible code that used sequential or modulated illumination, multiple illumination sources, and/or forms of spectral filtering to add further layers of security and authentication to the code.